Received a reply on Reddit that (mostly) solves the issue. As follows:
Still having a slight issue with L & R bumper buttons for some reason though.
Left C button, comes up as "3" in RA, and is mapped to "Right Analogue (Left)" - Works as intended as Left C in game.
Yet...
L button, comes up as "4" in RA, and I've mapped it to "L Button (Shoulder)" - For some reason does not function as L button should, instead functions as Left C.
Same goes for R button, comes up as 5, mapped to R button (shoulder), but in game acts as Right C.
I'm testing this in GooldenEye, where in the controller section in that pause menu you can test your button inputs.
It's weird.